1. Field of the Invention
The present invention relates to a narrow gap magnetoresistive (MR) read head and more particularly to an MR read head where gap layers are narrow in an MR sensor region adjacent an air bearing surface (ABS) to provide good resolution and thicker outside of the MR sensor region to provide good insulation between lead layers and first and second shield layers.
2. Description of the Related Art
An MR read head includes an MR sensor which is sandwiched between first and second gap layers G1 and G2 which are in turn sandwiched between first and second shield layers S1 and S2. Lead layers are sandwiched between the first and second gap layers for providing a sense current to the MR sensor. Magnetic fields from a magnetic disk change the resistance of the sensor proportional to the strength of the fields. The change in resistance changes the potential across the MR sensor which is processed by channel circuitry as a readback signal.
An MR read head is typically mounted to a slider which, in turn, is attached to a suspension and actuator of a magnetic disk drive. The slider and edges of the MR sensor and other layers of the read head form an air bearing surface (ABS). When a magnetic disk is rotated by the drive, the slider and one or more heads are supported against the disk by a cushion of air (an "air bearing") between the disk and the ABS. The air bearing is generated by the rotating disk. The read head then reads magnetic flux signals from the rotating disk.
The capability of an MR head to read data recorded at high areal densities is determined by its trackwidth and its resolution. The trackwidth of an MR read head is the length of the active or sensing region for the MR sensor and is typically defined by photolithography and subtractive or additive processing. Resolution is determined by the gap of the read head which is the distance between the first and second shield layers at the ABS. Accordingly, this distance is the total of the thicknesses of the MR sensor and the first and second gap layers. For a 2 gigabit/in.sup.2 read head, a typical gap thickness is 200 nm with a sensor thickness of 40 nm. This means that each of the first and second gap layers are 80 nm thick. For a 5 gigabit/in.sup.2 head, the total gap thickness can approach as thin as 100 nm.
When the first and second gap layers G1 and G2, which separate the MR sensor from the first and second shield layers S1 and S2, become thinner, the linear resolution of read head becomes higher. A serious limitation on the thinness of the gap layers of the read head is the potential for electrical shorting between the lead layers and the first and second shield layers. The thinner a gap layer, the more likely it is to have one or more pinholes which expose a lead layer to a shield layer. Pinholes can significantly reduce the yield of a production run of MR read heads.
It is important to note that the only place where the gap layers have to be thin is in an MR region where the MR sensor is located. The gap layers can be thicker between the lead layers and the first and second shield layers. Accordingly, it would be desirable if each gap layer could be thin in the MR region to provide high linear resolution and thick outside of the MR region to provide good insulation between the lead layers and the shield layers. In the above mentioned patent application, this is achieved, within limits, by providing a back fill of gap material to the first gap layer to replenish the gap material which is etched away during definition of the MR sensor. After masking by photolithography, the MR sensor is typically trimmed by ion beam milling. The practice is to over etch to ensure that the MR sensor is well formed. The over milling reduces the thickness of the first gap layer all around the MR sensor. In order to allow for this reduced thickness and to ensure that the over milling does not intrude into the first shield layer, the first gap layer is made sufficiently thick. Accordingly, a limitation of the teaching in the above patent application is that the first gap layer must have a thickness between the MR sensor and the first shield layer which is sufficient to prevent milling into the first shield layer when the MR is defined by ion beam milling. After the MR is defined, the thickness of the first gap layer milled away is then filled in by additional gap material which is referred to as "backfill" in the patent application. There is a strongly felt need for a first gap layer thickness in the MR region which is not dependent upon how much the gap layer will be milled away during definition of the MR sensor.
A write head is typically combined with a read head. A write head has first and second pole tips at the ABS. The second pole tip is a critical element of the write head since it is the last pole tip to induce magnetic flux into a rotating magnetic disk. When thin film layers are deposited to form a combined write/read head, the second pole tip is located directly above the MR region. If the MR region is not planar, any unevenness will be replicated into the layer which forms the second pole tip. If side edges of the second pole are not well formed, the trackwidth of the write head gets fuzzy and the write head loses resolution. For instance, when the first and second lead layers are connected to the MR sensor by overlapping junctions, in the read head, steps are formed. The steps are undesirably replicated through the layers to the second pole tip. There is a strongly felt need for a more planar MR region which will allow construction of a high resolution second pole tip in a combined head.